Modern Semi-automatic pistols having a reciprocating slide mounted atop a frame typically have a slide stop mounted on the frame which works in conjunction with the slide to hold it in an open position after the last round is discharged. Such slide stops are often biased away from the slide and only engage the slide when they are forced into engagement by the follower of the magazine, which has a pawl that engages the slide stop. The slide stop engages a catch in the slide to hold it in the open position.
When an empty magazine is replaced by a full magazine the pawl of the follower of the full magazine does not engage the slide stop. The slide stop is held in engagement with the slide against its biasing force by friction between it and the surfaces of the catch which it engages, as well as the geometry of the interfacing surfaces, which can provide varying degrees of mechanical engagement. The slide may be returned to battery by disengaging the slide stop from the catch. A return spring within the frame then operates on the slide to move it into battery, stripping a round from the magazine and chambering the round. Intentional disengagement of the slide stop may be effected by drawing the slide back, thereby disengaging the slide stop from the catch which allows the slide stop to move away from the slide under its biasing force. The slide is then released and moves into battery under the force of the return spring. Another method of returning the slide to battery is to directly push the slide stop away from the slide, forcibly disengaging the slide stop from the catch. The slide will then move to battery under the force of the return spring.
It is desirable to avoid unintentional disengagement of the slide stop from the slide which allows the slide to unexpectedly move into battery. This may occur, for example, when a magazine is forcefully driven home into the magazine well of the pistol. The inertial forces of that action, combined with the biasing force on the slide stop, can sometimes overcome the friction between the slide stop and the catch and cause the slide stop to move away from the slide and thereby release the slide, which moves into battery. There are clear advantages to preventing such an occurrence.